Goldfish, Carassius auratus, a non-sex changing (gonochoristic) fish, exhibits gender-typical reproductive functions (behavior and GTH secretion). Heterotypical (opposite gender) behaviors do not normally occur, but can be induced in adults by hormone treatments which do not inhibit the ability to perform homotypical behaviors. Male-typical behavior also can be induced without defeminization by androgen treatment in gynogenetic Japanese crucian carp, Carassius auratus langsdorfii, which evolved as an all-female population. Androgen treatment can also induce male-typical GTH secretion in female goldfish and crucian carp. Such sexual plasticity is also observed in hermaphroditic (sex changing) teleosts which exhibit reproductive functions of both sexes during their lifetime. Results of goldfish and crucian carp studies, and the existence of naturally occurring hermaphroditism, suggest that teleosts, regardless of their reproductive strategy (hermaphroditism, gonochorism, or gynogenesis), may commonly possess a sexually bipotential brain.